Atrial fibrillation carries a significant risk for memory decline, even when stroke is not involved, a meta-analysis found.

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Atrial fibrillation carries a significant risk for cognitive decline, even when stroke is not involved, according to results from a meta-analysis.

Note that the risk was similar when researchers excluded cognitive impairment and analyzed the studies only for dementia.

Atrial fibrillation carries a significant risk for cognitive decline, even when stroke is not involved, a meta-analysis found.

In 14 observational and prospective studies of patients with or without stroke, the relative risk of cognitive impairment was 1.40 (95% CI 1.19 to 1.64), according to Jeremy N. Ruskin, MD, of Massachusetts General Hospital, and colleagues.

The risk was similar when researchers excluded cognitive impairment and analyzed the studies only for dementia, "which is more reliably diagnosed than cognitive impairment," (RR 1.38, 95% CI 1.22 to 1.56), they reported March 4 in the Annals of Internal Medicine.

Various analyses of these 14 studies resulted in similar risks for cognitive decline or dementia:

Patients without a history of stroke -- RR 1.34

Studies that excluded patients with a history of stroke -- RR 1.37

Seven cross-sectional and prospective studies that examined patients following stroke found Afib conferred more than twice the risk of cognitive impairment or dementia (RR 2.70), with a stronger association in prospective studies (RR 3.01).

There is prior evidence that atrial fibrillation is associated with memory decline and dementia, but study findings have been inconsistent, Ruskin and colleagues noted in their introduction. They also pointed out that few studies have found a link between Afib and dementia/cognitive impairment independent of stroke. So whether or not other factors are involved in mediating the cognitive risk is unclear, they said.

In the current meta-analysis, researchers included 21 studies. The primary outcome was cognitive impairment. The secondary outcomes were cognitive impairment and dementia.

Prospective studies were assessed for quality using seven objective criteria, while nonprospective studies were evaluated using six criteria. The "higher the number of criteria, the more favorable [the] methodological quality and less risk of bias."

The seven prospective studies were well done, the researchers said, but had variable ways of diagnosing atrial fibrillation. However, "no single criterion stood out as the main problem in these prospective studies."

The nonprospective studies had various problems including bias and poor methodological quality. But when researchers excluded studies that only met three or fewer quality criteria, the risk hardly changed (RR 1.32).

"Our findings suggest a significant association between [Afib] and cognitive impairment or dementia independent of stroke in patients with first-ever or recurrent stroke and in a broader population including patients with or without a history of stroke," Ruskin and colleagues concluded.

They said that it is important to understand the "underlying mechanisms that link [Afib] with cognitive impairment."

The link could be due to shared risk factors such as hypertension, congestive heart failure, and diabetes, but this hypothesis wouldn't explain the longitudinal studies that controlled for comorbidities and still found a correlation, researchers said.

It could be due to silent infarcts that build up over time and impact cognitive ability, they said, adding that the present meta-analysis does not rule out this possibility. However, one study used imaging to exclude patients with a history of stroke and still found a link between Afib and cognitive decline.

Researchers mentioned these "potential but unproven mechanisms" that could link Afib with cognitive problems:

Heartbeat variability and reduced cardiac output that lead to brain hypoperfusion

Proinflammatory state in atrial fibrillation

Periventricular white-matter lesions

The current meta-analysis has limitations including the heterogeneity of the prospective studies, potential bias in selecting studies, and the absence of imaging to confirm stroke in many studies.

The study was supported by the Deane Institute for Integrative Research in Atrial Fibrillation and Stroke at Massachusetts General Hospital, the Harvard Catalyst, and the Harvard Clinical and Translational Science Center.

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